ImageMagick and GD are 2 of the most widespread graphic software libraries on the market. They make the dynamic creation and editing of images and graphs on an internet site doable, so they must be present on a web server if you host your websites on it and you would want to have something different than static images with fixed dimensions. If ImageMagick and GD are present, you'll be able to edit any image in many different ways - create thumbnails, change the colors, flip it, blur it, etc. Naturally, these modifications are doable if the script app that you use on your site permits you to carry out such things. The 2 libraries could be used with various web development languages - PHP, Python, Perl, etc., and support more than one hundred widely used image formats which you shall be able to work with - PNG, PSD, JPEG, TIFF, GIF and more.